Circulating immune complexes have been detected in cancer patient sera utilizing antigen non-specific assays. The etiology and molecular nature of these complexes is not well understood. Methods of immune complex detection, utilizing monoclonal antibody containing tumor associated antigens, should reduce the complexity of interpretation of assay results and provide an unequivocal answer as to whether immune complexes containing tumor antigens play a role in the neoplastic disease process. Utilizing HPLC gel filtration and solid phase ELISA technology and monoclonal antibodies raised to human melanoma antigens from spent culture medium, tumor antigen containing complexes will be detected and the components characterized. The characterization will include: 1) molecular ratios of antigen to antibody; 2) the class of patient antibody; 3) detection and specificity of antiglobulin; and 4) molecular nature of tumor antigen as compared to the form in spent culture medium. A variety of solid phase reagents for affinity isolation of tumor antigen containing immune complexes will be tested. These include soluble protein A, purified human Clq and monoclonal antibody to C3b, IgM, IgG, and melanoma associated antigens. Sera utilized for isolation and characterization of tumor antigen containing complexes will be pretested by four antigen non-specific assays for immune complexes, including the Clg, binding and Raji cell radioimmunoassay.